Carbohydrate antigens often occur in combination with human diseases. For instance, aberrant glycosylation is a typical hallmark of cancer cells, thereby creating new carbohydrate structure that are absent from or rarely present on normal human cells. Those carbohydrate structures were believed to be suitable candidates for the generation of tumor vaccines, but the carbohydrate itself are poorly immunogenic structures classified as T cell independent antigens. Therefore, vaccine development focused on the generation of synthetic carbohydrate based anti-tumor vaccines, whereby carbohydrate epitopes are coupled to immune potentiating carrier structures or natural proteins or oligopeptides (such as MUC1) and combined with additional adjuvances for the induction of an immune response especially for the induction of a cellular immune response. Polysaccharide are linked to immunogenic polypeptides such as tetanus or diphtheria toxoid or KLH or T helper epitopes in order to alter the immune response from T cell independent to T cell dependent in order to generate immunological memory. The production of such vaccines is extraordinarily difficult and expensive. Furthermore, such vaccines represent non-natural or artificial antigens with unknown or adverse side effects.
Until recently it was believed that carbohydrates are not presented by antigen presenting cells (e.g. dendritic cells) to immune effector cells and do not mediate a T cell immune response.
Now few reports show that complex carbohydrate are not removed during processing of glycoproteins by antigen presenting cells and can be presented to major histocompatibility complex II restricted T cells together with the peptid.
In the case of the MUC1 antigen, internalization, processing and presentation of glycopeptides on dendritic cells could be shown. MUC1 bearing short sialylated carbohydrates induced activation and maturation of dendritic cells phenotypically similar to that induced by bacterial LPS thereby lacking specificity, but these DCs were not capable of inducting a Th1 type immune response after coculture with allogenic CD4+ T cells or cytotoxic CD8 responses (Carlos et al. (2005) J Immunol 175: 1628-1635).
MUC1-derived peptides O-glycosylated with a Tn epitope induce cellular immunogenicity in mice, but immunization with glycopeptide-loaded dendritic cells showed no immunotherapeutic effect, no selective lysis of human MUC1 expressing murine cell lines and the elicited CTLs showed cross-reactivity between glycosylated and non-glycosylated forms of the same peptides, so the immune response was not effective and not CH-specific (Stepensky et al. (2005) Clin Exp Immunol 143:139-149).
Cancer associated MUC1 carrying short sugar moieties from mono- to tetrasaccharides (such as the tumor antigens Tn, TF, S-Tn, and S-TF) can even induce suppression of human T cell responses (Agrawal et al. Nat Med 1998 January; 4(1):43-9).
Bacterial glycosylation is completely different from eukaryotic glycosylation due to a different profile of enzymes involved in the glycosylation machinery. The majority of the polysaccharides of bacteria are negatively charged polysaccharides which clearly fail to activate T cells and hence are generally classified as T cell independent type 2 antigens. More recently it was described that zwitterionic capsular polysaccharides from certain bacteria have the ability to activate CD4+ T cells. However, MHCII restriction for zwitterionic polysaccharide antigens is not clear, and the T cells are activated in a polyclonal non-antigen specific fashion which is not antigen or epitope specific but show a broad Vβ usage and cross-reactivity apparently resembling the broad activation induced by mitogens (Cobb and Kasper, Cell Microbiol 2005; Eyon, Zenewicz, Flavell, Cell, 2005).
Furthermore, carbohydrates and carbohydrate antigens are generally known as weak immunogens.
Th1 type immunity is considered to be important and necessary in tumor rejection and in elicitation of potent immune responses in various diseases (Kobayashi et al., 1998, J. Immunol. 160: 5869-5873). It was shown that some short tumor carbohydrates may be presented and recognized together with certain aminoacids as combined necessary binding motifs. However, this does not lead to a Th1 type immune response. In contrast, in case of MUC1 desialylated MUC1 (presenting short sugar moieties such as Tn or TF) fails to induce T cell cytokine production and hence no T cell activation or in case of sialylated sugars induction of the secretion of cytokines such as TNFalpha together with IL-6 which are connected with tumor metastasis, tumor progression and bad prognosis, occur and hence fail to activate the necessary TH1 response and is even thought to be connected with tumor escape from immune responses (Carlos et al., J. Immunol,).
This state of the art teaches that natural molecules comprising human carbohydrate tumor antigens can not induce a potent cellular Th1 and cytotoxic immunity directed against carbohydrate epitopes, and that polysaccharides from bacteria, in particular the capsular polysaccharides, can not induce an antigen specific immune response.
Hence, the use of these carbohydrate molecules would not be suitable for tumor vaccine approaches using (i) dendritic cells for presentation of the carbohydrate antigens which would not induce a potent cytotoxic immune response when administered in humans and not be suitable for tumor vaccine approaches using (ii) APC such as DC for presentation of the carbohydrate antigens for generation of antigen specific T cells in a Th1 response for a adoptive T cell therapy in patients.
However, due to the importance of carbohydrate antigens in the development of pathologic diseases such as cancer, it would be advantageous to obtain means for inducing an effective carbohydrate-specific cellular immune response.
It is the object of the present invention to provide respective means.